Wear resistant materials are often used in coating or hardfacing applications to protect the underlying material from rubbing, impact, frictional wear and similar potentially damaging mechanical actions. Wear resistant coatings or hardfacings may include a layer of uniformly hard or wear resistant material. However such materials are often expensive and may not be readily susceptible to forming coatings on their own. For this reason, one strategy for developing wear resistant coatings is to incorporate a hard phase into a material that is more susceptible to coating or a hardfacing processes and that is more cost effective. Often, producing an effective wear resistant coating material may require incorporating a high volume fraction of the hard phase into the coating material.
The hard phase, or domains of wear resistant material dispersed in the wear resistant coating, are often ceramic materials. Ceramic materials that are especially suitable generally have chemical structures that involve electron transfers leading to very strong ionic (although in some cases covalent) bonding. The result is very stable, strong and high melting point compounds.
Conventionally, wear resistant coating materials are ceramic, metallic, or polymeric material incorporating the hard phase. For example, the hard phase may be incorporated into an iron based alloy. The iron-based alloy allows the coating to be applied to a substrate while the hard phase provides the wear resistant characteristics. In the case of ceramic hard phase materials, the hard phase may be provided as particles dispersed in the ceramic, metallic, or polymeric matrix.
Recently, a great deal of research and development has been directed at developing wear resistant thermal spray and hardfacing alloys that incorporate carbide materials into a ductile matrix. Carbides, such as tungsten-carbide (WC), titanium-carbide (TiC), chromium-carbide (Cr3C2), and the like have been used as hard phases within ductile matrices such as cobalt, iron, or nickel. As in the general paradigm for wear resistant coatings, the ductile component allows a cost effective coating to be formed on a substrate, while the carbide material provided the desired wear resistance.
Other wear resistant coatings have been developed from hard oxides. For example, titanium oxide (TiO2), zirconium oxide (ZrO2), aluminum oxide (Al2O3), etc. have all been used to form wear resistant coatings. As with coatings incorporating carbide hard phases, oxide hard phases may be incorporated into a metal matrix. Additionally, oxide based coatings have also been produced by densifying the hard oxides to form a ceramics.
In addition to carbides and oxides, some use has also been made of titanium boride (TiB2) and zirconium boride (ZrB2). As with carbides and oxides, wear resistant coatings including titanium boride and zirconium boride are generally formed by providing a titanium boride or a zirconium boride hard phase in a metallic, ceramic, or polymeric matrix.